Species in tropical rainforests will still go extinct even if deforestation is stopped immediately, unless efforts are made to restore damaged areas.

This is the conclusion of research led by a team at Imperial College London, looking at ‘deforestation lag’. Deforestation causes species to go extinct as their habitat shrinks, but it takes time for habitat loss to take full effect.

The study, published today in Current Biology, modelled what would have happened if deforestation across the tropical regions of the Amazon, Congo and southeast Asia had halted in 2010. It suggests that 140 vertebrate animals, such as rats and reptiles, would still go extinct in the future as a result of the forest clearance that had already taken place.

Invertebrate species, such as worms and insects, which play critical roles in forest ecosystems, would also likely become extinct in spite of deforestation halting, but their loss is harder to quantify.

Deforestation does not cause extinction of a species immediately, as the animals that remain try to adapt to their changed environment. Lead author of the study Dr Isabel Rosa of Imperial’s Department of Life Sciences said: “The lag between the deforestation event and species extinctions causes ‘deforestation debts’, which build up over time, as more and more deforestation takes place. These still need to be paid, even after forest loss has stopped.”

Many conservation efforts focus on preserving untouched forests, and while this will help prevent further losses, Dr Rosa says this is not enough, and more must be done to save those already affected by deforestation.

“Protecting untouched forests prevents more damage, but cannot help the species already on the brink of extinction. Instead, we need to complement preservation with restoration of areas damaged by forest clearance,” she said.

“With restoration, we can avoid paying some of the deforestation debt and save species otherwise doomed to extinction.”

Carbon emissions

As well as continuing species losses, the study also suggests carbon emissions will continue after deforestation stops. As biomass like trees and leaves decay following deforestation, it releases carbon dioxide, which contributes to global warming.

The team calculated that if deforestation stopped in 2010, another 5-10 years of total carbon emissions from tropical forests would still be released from the debt of decaying wood. This effect means that in Brazil - where deforestation of the Amazon was reduced by 30 per cent between 2005 and 2010 - there was only a 10 per cent reduction in carbon emissions over the same period.

Restoring damaged habitats would also help mitigate this deforestation debt, as restoring vegetation would allow some of this excess carbon to be taken up by new trees rather than emitted into the atmosphere. Restoration is therefore effective at both reducing species loss and preventing extra carbon emissions.

To estimate these debts, the team modelled historical patterns and rates of deforestation in the tropical regions of the Amazon, the Congo basin and southeast Asia. They then estimated carbon emissions and species losses and compared them to other estimates.

With this, they calculated the lag time between areas becoming deforested and associated species that depended on the forest going extinct, as well as the rate of carbon emissions.

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'The Environmental Legacy of Modern Tropical Deforestation' by Rosa et al. is published in Current Biology.